1. Field of the Invention
The present invention relates to a combustion chamber of an internal combustion engine of the type in which fuel oil is injected directly into the combustion chamber. More particularly, it is concerned with a combustion chamber of an internal combustion engine which permits the use of volatile fuels of low cetane number such as gasoline and alcohol.
2. Description of the Prior Art
Generally, a known technique which permits the use of coarse fuels, e.g. methanol (methyl alcohol), is described in Japanese Utility Model Laid Open No. 107820/1982. According to this proposed construction, as shown in FIG. 5 of the accompanying drawings hereof, a precombustion chamber (b) is provided laterally at the top of a cylinder (a), a preheating plug (d) is disposed obliquely in a bottom wall portion (c) of the precombustion chamber (b), further a fuel injection valve (e) is disposed opposite the preheating plug (d), and a spark plug (f) is disposed between the fuel injection valve (e) and the preheating plug (d).
In the above described construction, a glow plug is used to raise the temperature in the precombustion chamber to ignite the burn fuel in order to improve the engine start-up characteristic and drivability under a low load condition.
However, since the precombustion chamber (b) of the cylinder (a) is in communication with a main combustion chamber (g) of a piston (i) through a throat (h), a throttle loss at the time of introducing compressed air into the preheating chamber (b) and a heat loss at the time of flowing of combustion gas from the precombustion chamber (b) into the main combustion chamber (g) are large, thus causing deterioration of the thermal efficiency.
Such deterioration of the thermal efficiency results in a reduction of fuel combustion in the combustion chamber, and a corresponding lowering of output and the formation of unburnt material such as HC. Further, at the time of start-up at a low outside air temperatures of -20.degree. C. or lower, it is necessary to take countermeasures such as enhancing the heat generating ability of the glow plug to an extreme degree or prolonging the heating time in order to permit ignition with the spark plug and combustion without misfire because the fuel oil injected is methanol which is poor in volatility and also because the amount of fuel oil is increased at the time of the start-up of the engine. This is undesirable from the standpoint of battery capacity and start-up time.